For much of the sixteenth-century, France was wracked with religious strife, as the Wars of Religion pitted Catholic against Protestant. Whilst the conversion of Henri IV to Catholicism ended much of the conflict, the ensuing peace highlighted the fractious nature of French Catholicism and the many competing threads that ran through it. This book investigates the gradual division of the French Catholic reform movement, often associated with those known as the 'devots' during the first half of the seventeenth century. Such division, it is argued, was emerging before the publication in France (1641) of the posthumous 'Augustinus' of Jansenius, not simply as a sequel to that. Those who were already distinguishing themselves from other 'devots' before that date were thus not yet identifiable as 'Jansenists'. Rather, the initial defining sentiment was increasing French hostility towards Jesuit involvement in Catholic Reform, both at home and abroad. Drawing on sources from the Jesuit archives in Rome and on Port-Royal material in Paris, the book begins with an investigation into the development of Catholic Reform in France, showing the problems that emerged before 1629 and the degree to which these were or were not resolved. The second half of the book contrasts the fragmentation of the movement in the years beyond 1629, and the context of Richelieu's new directions in French foreign policy. Covering a crucial period in the lead up to the establishment of an absolute monarchy in France, this book provides a rich new explanation of the development of French political and ecclesiastical history. It will be of interest not only to those studying the early modern period, but to anyone wishing to understand the roots of French secular society.